1. Field of the Invention
The present invention is directed to a process for purifying laurolactam by an integrated connection of distillation and crystallization. The crystallization may be performed as a solution or melt crystallization. The stream from which the laurolactam is isolated may comprise, in addition to the laurolactam, at least one component other than laurolactam which may have a lower or higher boiling point than laurolactam. More specifically, the stream may be a laurolactam synthesis stream comprising laurolactam, a mother liquor, synthesis starting materials and low, mid- and high boiling fractions.
2. Description of the Related Art
Laurolactam is typically purified by means of a multistage distillation in which secondary components with higher and lower boiling points are removed from the laurolactam. Conventionally, such distillation processes employ application of reduced pressure, due to the high boiling point of laurolactam. As a result of thermal stress on a laurolactam mixture in conventional purification methods, partial thermal decomposition of the laurolactam, resulting in overall yield reduction and high production cost, is experienced.
The “conventional” process for synthesis and isolation of laurolactam is described in Ullmann's Encyclopedia of Industrial Chemistry (2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 10.1002/14356007.a08—201), in the article: “Cyclododecanol, Cyclododecanone, and Laurolactam” by Thomas Schiffer and Georg Oenbrink